In our previous report, it was discovered that the polycondensation of 9-amino-nonanoic acid follows second order from the beginning up to the extent of reaction, p, around 99%, and after which the reaction changes rapidly to third order. In this paper, we wish to report that this change of the reaction order from second to third occurred also in the polycondensation of 6-aminocaproic acid and 11-amino-undecanoic acid. The transition region lay again at p around 99%. It may be concluded that this is a general rule in the polycondensation of the ω-amino-acids (monomers of the A—B type), and the controversial results that appeared in the literature may be cleared up by our experiments. 相似文献
A mild and facile Wittig reaction between N‐substituted maleimides and aldehydes has been developed. Various synthetically valuable alkylidenesuccinimides were obtained from this one‐pot reaction in high yields (up to 99%). The product was obtained by simple filtration and no extra purification was necessary. Ethanol, an environment‐benign solvent, was found to be a suitable reaction medium. 相似文献
γ-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter synthesized in the central nervous system from glutamate
by glutamate decarboxylase (GAD). It has applications in the production of many drugs. The technology of GABA synthesis by
treating L-glutamic acid with the cells of the gene-engineered GAD superproducer strain of Escherichia coli GAD K10 was developed. Cell growing in the presence of 0.02 mM pyridoxal phosphate (PLP) causes the 2- to 2.5-fold increase of total productivity of the cells. The best way to prepare
the cells for the reaction was their thermal activation by pretreatment for 1 h at 53°C. The optimal conditions for this reaction
were 37°C and pH 4.6. The rate of the enzymatic reaction is the function of acetate concentration with the maximum at 0.5
M acetate. The total amount of GABA synthesized using 1 g of wet cells reached 23–25 g. The final concentration of GABA in
the reaction medium was 280–300 g/L. The yield of the product was about 99%. 相似文献
The aim of the current study was to design a nucleotide-based radiopharmaceutical which could be labeled with 99mTc and to investigate its radiopharmaceutical efficiency and stability. GHA (glucoheptonate) was used as bifunctional chelate.
GHA was labeled with 99mTc by SnCl2 reduction method first, and then G (guanine) was conjugated with 99mTc-GHA at 90 °C. In order to determine its radiopharmaceutical stability, thin layer radio chromatography (TLRC) and electrophoresis
were employed. In addition, the results were confirmed using high performance liquid radio chromatography (HPLRC). Scintigraphic
imaging was performed on rats with mammary tumors, while tissue distribution was determined on Albino Wistar rats. Labeling
yield was found to be over 95% and the labeled complex maintained its stability during the study period. The lipophilicity
of the 99mTc-GHG was measured and the partition coefficient (logP) of the labeled compound calculated. The results demonstrated that the uptake of 99mTc-GHG (99mTc-glucoheptonate-guanine) reached its maximum at 3 hours p.i. in stomach and intestines. Main way of excretion was renal.
Hepatobiliary excretion was also observed. In conclusion, 99mTc-GHG may be useful as a nucleotide-based radiopharmaceutical for in vivo applications. 相似文献
Summary This investigation focused on the labeling of pefloxacin, a fluoroquinolone antibacterial agent, with 99mTc to form 99mTc-pefloxacin complex. The labeling process was done by direct addition of pertechnetate in isotonic solution to Sn-pefloxacin solution. The labeling technique is effective, as a high labeling yield (98%) was obtained after 30-minute reaction time. Different factors were found that influenced this labeling reaction: 0.5 mg pefloxacin or more must be used to prevent the formation of colloids in the reaction medium. Fifty micrograms of stannous chloride dihydrate were found to be sufficient to reduce all pertechnetate with activity ranging from 37 to 3700 MBq without the detection of free pertechnetate or colloids in the reaction mixture. The pH of the reaction medium was found to play an important role in the labeling process. The labeling reaction proceeds well at neutral pH (pH 6) but at acidic pH value (pH 4 or below) the yield of 99mTc-pefloxacin complex decreased markedly to a labeling yield of 5%. The reaction mixture must be heated to 100 °C in an oil bath to enhance the formation of the 99mTc-pefloxacin complex. The biodistribution data show that 99mTc labeled pefloxacin was retained in infectious focus. The retention was specific since the abscess uptake of 99mTc-pefloxacin remained high as compared to the uptake of aseptic foci at 24-hour post injection. Also, the clearance of the tracer from other tissues is rapid on the contrary to its clearance from the septic focus. This supports the hypothesis that 99mTc-pefloxacin is retained at the infectious site because of its specific binding to the gyrase enzymes of bacterial cells. 相似文献
A highly efficient asymmetric cascade reaction between keto esters and alkynyl alcohols and amides is reported. The success of the reaction was attributed to the combination of chiral Lewis acid N,N′‐dioxide nickel(II) catalysis with achiral π‐acid gold(I) catalysis working as an asymmetric relay catalytic system. The corresponding spiroketals and spiroaminals were synthesized in up to 99 % yield, 19:1 d.r., and more than 99 % ee under mild reaction conditions. Control experiments suggest that the N,N′‐dioxide ligand was essential for the formation of the spiro products. 相似文献
Slow addition of a primary amine to the reaction mixture greatly increases the scope of the titanium-catalyzed asymmetric reduction of imines 1 . An important added feature of this method is that chiral secondary amines 2 can be obtained in much higher optical purity (up to 99 % ee) than would be predicted from the E:Z ratios of the starting imines 1 . 相似文献
N,N′‐Dioxide/nickel(II) complexes have been developed to catalyze the inverse‐electron‐demand hetero‐Diels–Alder reaction of β,γ‐unsaturated α‐ketoesters with acyclic enecarbamates. After detailed screening of the reaction parameters, mild optimized reaction conditions were established, affording 3,4‐dihydro‐2H‐pyranamines in up to 99 % yield, 99 % ee and more than 95:5 d.r. The catalytic system was also efficient for β‐substituted acyclic enecarbamates, affording more challenging 2,3,4‐trisubstituted 3,4‐dihydro‐2H‐pyranamine with three contiguous stereogenic centers in excellent yields, diastereoselectivities, and enantioselectivities. The reaction could be scaled up to a gram scale with no deterioration of either enantioselectivity or yield. Based on these experiments and on previous reports, a possible transition state was proposed. 相似文献
The enantioselective aldol reaction between ketones and aldehydes constitutes one the most common reaction models for the evaluation of novel organocatalysts. The last few years, it has been shown that the organocatalytic aldol reaction can be performed in water. A family of tripeptides consisting of proline, phenylalanine, and tert-butyl esters of amino acids was successfully employed in this asymmetric transformation. The products of the reaction between various ketones and aldehydes were obtained in high yields (up to 99%) with excellent diastereo- (up to 97:3 dr) and enantioselectivities (up to 99% ee). The C-terminal amino acid determines the ability of the tripeptide (Pro-Phe-AA-OtBu) to act efficiently in aqueous or organic medium. 相似文献
Ionic liquids were tested as the reaction media for hydrogen transfer reduction of substituted acetophenones and some other
ketones with the [RuCl(TsDPEN)]2 complex as the catalyst. Reactions were going well and faster than in common solvents. Corresponding alcohols had high ees in the case of aryl alkyl ketones, but just medium ees were reached in the case of dialkyl or unsaturated ketones. An interesting phenomenon was observed, namely that rise of
the reaction temperature did not have negative influence on the ee of the reaction product. 相似文献
Analysis of the mass balance equations that describe a reaction system may be useful to provide information about its dynamics, such as the restricted set of compositions that can be achieved from a given set of initial compositions and the effect of feeding reactants to the reaction environment along the reaction course. Since these results may be important for the formulation of reaction policies, this work presents the properties of a matrix polymerization model previously developed and extended to describe transient conditions. This model is based on the definitions of two matrices: the consumption matrix ( A − Kt ), which contains information about chemical transformations among the many active polymer species in the system, and the propagation matrix Kp , which contains information about chain growth. It is shown that the set of mass balance equations that describes the dynamics of active chemical species in polymerization reactions has a stable and unique solution, which is bounded if feed rates are also bounded. It is also shown that the set of compositions that may be reached through manipulation of the feed rates is restricted and may not include all possible chemical compositions. Finally, it is shown that the obtained molecular weight distributions are special multiple time convolutions of the initiation rates.
2,2′-[(8-hydroxyquinolin-7-yl)methylazanediyl]diacetic acid (HQMADA) was synthesized via reaction of 8-hydroxyquinoline with
iminodiacetic acid in presence of paraformaldehyde with a yield of 27%. The obtained compound was well characterized via different
analytical techniques. Labeling of the synthesized compound with technetium-99m in pertechnetate form (99mTcO4−) in the presence of stannous chloride dihydrate was carried out via chelation reaction. The reaction parameters that affect
the labeling yield such as HQMADA concentration, stannous chloride dihydrate concentration, pH of the reaction mixture, and
reaction time were studied to optimize the labeling conditions. Maximum radiochemical yield of 99mTc-HQMADA complex (91.9%) was obtained by using 1.5 mg HQMADA, 50 μg SnCl2·2H2O, pH 8 and 30 min reaction time. Biodistribution studies in mice were carried out in experimentally induced infection in
the left thigh using E. coli. 99mTc-HQMADA complex showed higher uptake (T/NT = 5.5 ± 0.3) in the infectious lesion than the commercially available 99mTc-ciprofloxacin (T/NT = 3.8 ± 0.8). Biodistribution studies for 99mTc-HQMADA complex in Albino mice bearing septic and aseptic inflammation models showed that 99mTc-HQMADA complex able to differentiate between septic and aseptic inflammation. 相似文献
A stable asymmetric intramolecular Povarov reaction has been established to provide an efficient method to access structurally diverse trans,trans-trisubstituted tetrahydrochromeno[4,3-b]quinolines in high stereoselectivities of up to >99:1 diastereomeric ratio and 99 % enantiomeric excess, without any purification step. Additionally, to facilitate large-scale application of this method, a low catalyst loading protocol was employed, 0.2 mol % chiral phosphoric acid, which provided the cycloadducts without any loss in yield and enantioselectivity. Theoretical studies revealed that the reaction occurred through a sequential Mannich reaction and an intramolecular Friedel–Crafts reaction, wherein the phosphoric acid acted as a bifunctional catalyst to activate the para-phenolic dienophile and N-2-hydroxy-2-azadiene simultaneously. 相似文献
Virtually all members of the order Thermotogales have demonstrated the ability to produce hydrogen; however, some members of this order produce considerably greater quantities
than others. With one representative of this order, Thermotoga neapolitana, we have consistently obtained accumulation of 25–30% hydrogen with 12–15% carbon dioxide as the only other prominent product
in the batch reaction. In contradistinction to information widely disseminated in the literature, we have also found that
most members of this order tolerate and appear to utilize the moderate amounts of oxygen present in the gaseous phase of batch
reactors (6–12%), with no apparent decrease in hydrogen production. Hydrogen accumulation has been widely reported to inhibit
growth of Thermotogales. While this may be true at very high hydrogen tensions, we have observed log phase bacterial morphology (rods) even in the
presence of 25–35% hydrogen concentrations. To maximize hydrogen production and minimize production of hydrogen sulfide, inorganic
sulfur donors are avoided and the cysteine concentration in the medium is increased. We and others have demonstrated that
different members of the order Thermotogales utilize a wide variety of feedstocks, including complex carbohydrates and proteins. Thus, it appears that organisms within
this order have the potential to utilize a variety of organic wastes and to cost-effectively generate hydrogen. 相似文献
A new BINOL‐derived chiral phosphoric acid bearing 2,4,6‐trimethyl‐3,5‐dinitrophenyl substituents at the 3,3′‐positions was developed. The utility of this chiral phosphoric acid is demonstrated by a highly enantioselective (ee up to >99 %) and diastereoselective (syn/anti up to >99:1) asymmetric Mukaiyama–Mannich reaction of imines with a wide range of ketene silyl acetals. Moreover, this method was successfully applied to the construction of vicinal tertiary and quaternary stereogenic centers with excellent diastereo‐ and enantioselectivity. Significantly, BINOL‐derived N‐triflyl phosphoramide constitutes a complementary catalyst system that allows the title reaction to be applied to more challenging imines without an N‐(2‐hydroxyphenyl) moiety. 相似文献
Enzymatic regioselective acylation of 5-azacytidine with vinyl laurate was successfully conducted with an immobilized lipase
from Candida antarctica type B (i.e., Novozym 435) for the first time. The acylation of 5-azacytidine took place at its primary hydroxyl group and
the desired product 5′-O-lauroyl-5-azacytidine could be prepared with high reaction rate, high conversion, and excellent regioselectivity. The influences
of several key variables on the enzymatic acylation were also systematically examined. Pyridine was found to be the best reaction
medium. The optimum initial water activity, the molar ratio of vinyl laurate to 5-azacytidine and reaction temperature were
0.07, 30:1, and 50 °C, respectively. Under the optimized conditions described above, the initial reaction rate, the substrate
conversion, and the regioselectivity were as high as 0.58 mM/min, 95.5%, and >99%, respectively, after a reaction time of
around 5 h. 相似文献